For the purposes of wireless telecommunication, national and international bodies assign frequency bands (or channels) within the radio spectrum for specific uses, and in most cases, license the rights to these channels. Some specific parts of the spectrum may not be used by licensed services in a specific location at a specific time. Local regulatory authorities typically control and authorise the use of white-space in their own respective regions, and the available “white-space” bandwidth will therefore vary from country to country.
On the 4 Nov. 2008, the Federal Communications Commission (FCC) approved the use of vacant/unused portions of the broadcast spectrum in the 54 MHz-698 MHz range by unlicensed devices for fixed and personal/portable use. These vacant/unused portions of the spectrum are known as “white spaces”. These became available for “unlicensed secondary use” after the switchover to digital TV broadcast. The FCC has also defined numerous safeguards in order to protect services and service providers against harmful interference of white spaces devices.
Firstly, all unlicensed white-space devices must include geographical location technology that allows the device to determine its location and to match the current location of the device against a pre-existing database of available channels corresponding to that geographical area.
FIG. 1 illustrates a channel availability database as presently known in the art. In essence, such databases cross reference geographical areas with white-space channels available for use within specific sub-regions of that geographical area. For example, a geographical area (such as a country, country state, etc) may be dissected or subdivided into a plurality of sub-regions within the database. Each of these sub-regions may have a specific set of white-space channels that may be usable within that sub-region. This is illustrated in FIG. 1, whereby each sub-region (denoted by the boxed areas in the database grid) contains an indication whether channel/band ‘A’ and/or ‘B’ is available for use within each particular sub-region. Geographical areas and channels recorded by these databases are, at least in some current channel availability databases (such as those in the US), divided up so as to be denoted by rectangular (e.g. 50 m-by-50 m or 100 m-by-100 m) geographical sub-regions or grid points (as in this example the channel availability database is in the form of a grid, with each geographical sub-region being a regular shaped grid point or box). In the US at least, this is to be in conformity with current FCC rulings, but other regions may have different standards and implement their availability database(s) differently.
These databases operate on the principle that, if the geographic location of a particular white-space device is known, then the channels available for use by that white-space device can be identified by comparing the geographical location of the white-space device to the geographical area represented by the database. Where the geographic location of the white-space device matches up/overlaps with one or more geographical sub-regions, the channels available for use by that white-space device being in the particular determined geographical location are thereby determined.
Secondly, according to the FCC ruling, all unlicensed white-space devices must access such a channel availability database to determine channels that they are allowed to operate on before they begin white-space transmission or operation. WSDs must therefore transmit and inform their determined geographic location when querying with such databases.
For example, some white-space devices may determine their location via an onboard GPS system, or they may utilise local Wi-Fi networks to establish their position. Others may actually be geographically fixed and therefore they know their exact location anyway. Typically, the geographic location of the white-space device is encoded using Geography Markup Language (GML) which is a standard used to universally encode and transmit geographical location of such devices. There are many methods known in the art for determining the geographical location of such devices and, as such, will not be discussed at length here.
When a white-space device sends its location to the database via query signalling, the database can verify which channels are available for use within the area the white-space device has identified it is located in. The database should only inform the white-space device of channels that can be used without interference with other devices, primary users of such devices and protected entities (for example, entities/devices operating on frequencies/bandwidths that are already allocated to a particular use). This may sometimes entail informing a white-space device that no channels are available where necessary.
The FCC also requires new unlicensed white-space devices to include spectrum-sensing technology allowing them to detect the presence of other signals in their vicinity. For example, to detect if there are other localised wireless transmission/reception sources in their vicinity that the white-space devices could interfere with if they operated on these frequencies. Such information is constantly in flux and unpredictable, and therefore is not typically logged in a channel availability database. Therefore the white-space devices must conduct their own localised survey of their location/area to verify white-space channels suitable for them to operate over.
On start-up, white-space devices will query the database with their current location (likely gleaned from GPS or mobile telephone triangulation) and will receive in response a list of frequencies that can (and/or cannot) be used within their local area. The available channel availability data provided from the database may then be stored on the memory of the device.
It is well known that there is frequently an element of inaccuracy when measuring geographic location. To compensate for this in the prior art, when the database receives a geographic location of a white-space device, it automatically assumes a default inaccuracy/uncertainty to this geographic location. At present, to be in conformity with present FCC standards/rulings, a default uncertainty of ±50 m is to be assumed for each reported geographic location. This uncertainty in the location of the white-space device is shown in FIG. 1. This effectively translates as meaning that the white-space device may actually be located anywhere within the default uncertainty area (denoted by the annotated circle). This means that, when the database is identifying which channels are available for use, the database must consider all of the geographic sub-regions that the white-space device could be located in. As such, the only channels that can be identified as available are those that are common to all these possible geographic sub-regions that the white-space device could be located in.
This is a problem in many situations. For example, if the device is actually physically located in a geographic sub-region that has channels A & B available to the device, but the default uncertainty overlaps with another sub-region that only has A available, then the database can only identify channel A as available and suitable for use by the white-space device. This can result in an inefficient use of the available channels and can place unnecessary restrictions on such white-space devices (for example, on bandwidth).
This problem is further compounded in situations such as in FIG. 1, where it can be seen that there is no common channel across all sub-regions that the white-space device could be located in (based on the default uncertainty assumption). In such a scenario, the white-space device would be incapable of operating, despite being actually physically located in a region that allows for operation in bands A & B, resulting in an inefficient use of the available channels/spectrum.
The listing or discussion of a prior-published document or any background in this specification should not necessarily be taken as an acknowledgement that the document or background is part of the state of the art or is common general knowledge. One or more aspects/embodiments of the present disclosure may or may not address one or more of the background issues.